1. Field of the Invention
This invention relates to multicelled gas discharge display/memory devices and more particularly to methods of operating such devices with preferred wave forms for addressing and sustaining functions which simplify the circuitry associated with the devices.
2. Description of the Prior Art
Multicelled gas discharge devices as display and/or memory units have been proposed in the form of a pair of opposed dielectric charge storage members which are backed by electrodes, the electrodes being arranged in a first and second array which are so oriented with respect to an ionizable gaseous medium as to define discharge sites in the gas between electrodes separated from the gas by dielectric. Commonly, the devices are arranged with the electrodes of the first and second arrays transversely related, either on opposite sides of a thin volume of the gaseous medium, as disclosed in Baker et al. U.S. Pat. No. 3,499,167 which issued Mar. 3, 1970, or on the same side of a volume of the gaseous medium, as by the presence of cavities in the dielectic between transverse electrodes embedded in the dielectric as disclosed in Schermerhorn U.S. Pat. No. 3,787,106 which issued Jan. 22, 1974. Charged particles (electrons and ions) produced upon ionization of the gas volume of a selected discharge site, when proper alternating operating voltages are applied across the gas and dielectric between opposed electodes, are collected upon the surface of the dielectric at specifically defined location and constitute an electrical field opposing the electrical field which created them. Those collected charges present a wall voltage on the dielectric which augments an applied voltage of the polarity opposite that which caused their collection so that the potential across the intervening gas is sufficient to again initiate a collection of charges on the dielectric walls. This repetitive and alternating charge collection and ionization discharge constitutes an electrical memory of a cell or site in the "on" state of discharge. With properly chosen values of the alternating voltage, cells or sites in the "off" state of discharge remain in that state during the alternations, hence that state is also retained in electrical memory.
The alternating voltage offering the above memory characteristics is termed a "sustaining voltage". For a given device it usually has a range of values. Current forms of panel devices typically operate with sustainer voltage transitions of about 95 volts on either side of a neutral level where a delectric overcoat of magnesium oxide is interfaced with the gaseous medium as disclosed in Hoehn et al., U.S. Pat. No. 3,863,089 which issued Jan. 28, 1975 and the gaseous medium is typically about 99.9 percent atoms neon and 0.1 percent atoms argon at a pressure of from 0.2 atmospheres to about 1 atmosphere and the discharge gap is of 4 to 6 mils.
Conventionally the sustainer voltage applied across a device has been made up of components applied to each electrode array as with switching circuits referenced to a common point, frequently ground. A fixed or variable period has been proposed for the sustainer. Addressing of selected discharge sites has been accomplished by augmenting voltage signals superimposed on and thus referenced to the pulsating voltages of the sustainer components. In Schmersal U.S. Pat. No. 3,803,449 which issued Apr. 9, 1974 there is disclosed a sustainer controlled system wherein the sustainer component to individual selected electrodes or groups of electrodes is imposed for a time duration which is selected in accordance with discharge manipulation desired at a site. Lengthening the time duration of and/or increasing the magnitude of the high voltage interval of the sustainer imposed across a site places it in an "on" state of discharge while shortening the time duration of the sustainer pulse causes an erase discharge at the selected site. In Miller et al. U.S. Patent application Ser. No. 546,241 filed Feb. 3, 1975, now U.S. Pat. No. 3,993,990, a system is disclosed in which the sustainer was modified by contracting the time duration of that portion of a sustainer period which was not employed in a discharge manipulating function while lengthening the time duration of that portion which was utilized in the manipulation. Such changes were concerned with extending the time duration of addressing pedestal levels of the sustainer and imposed addressing voltage pulses on those pedestals for both write and erase functions.
Schmersal acheived a simplification in electronics by eliminating addressing driver circuits for the electrodes however his constant amplitude pulse square wave sustainer required individual electrode controls for the sustainer components. He sought to simplify such controls by employing a multiplexing approach. Thus while a regular sustainer cycle was applied to those electrodes outside the region of discharge manipulation certain electrodes associated with the region were subjected to partial select signals which were outside the select write or erase voltage margins of their sits. The full signals were applied only to discharge sites desired to be addressed. In the Miller et al disclosure the system employed bulk sustainer voltage sources for each array of electrodes, logic control of the bulk sustainers according to the discharge manipulation to be performed, and individual or multiplexed electrode address drivers for the write and erase function operating from floating sustainer voltages.
Schermerhorn U.S. Pat. No. 3,851,210 granted Nov. 26, 1974 employed asymmetric sustainer voltage components to manipulate discharge states of sites in a display/memory panel device. Interchange of the sustainer asymmetry between electrode arrays effectively shifted the neutral wall charge of the sites sufficiently to invert their discharge states. Discharge manipulation of but one form could then be employed as an addressing technique since, for example, an erase function could be used to terminate discharges in the normal operation of the device or to initiate discharges by erasing a site while the device was in an inverted discharge state and then reinverting the device to place that site in an "on" state of discharge.
The present invention facilitates the manipulation of discharge state at selected discharge sites in a display/memory panel device.
Another object of the invention is to simplify the drive circuitry for display/memory panel devices.
A third object is to simplify the logic interfacing to the addressing drives for display/memory panel devices.
A forth object is to adapt display/memory panel device operation to integrated circuit drive electronics.